Prompt previous tokens for streaming (#163)

* feat: prompt previous tokens for streaming

I used a vector pointer instead of vector itself because it gave weird errors, and why not

* convert vector to use with C api

* feat: remove old refs, check for prompt size

* feat: use better way of getting the pointer

whisper.h

@@ -208,6 +208,10 @@ extern "C" {
         bool speed_up;  // speed-up the audio by 2x using Phase Vocoder
         int  audio_ctx; // overwrite the audio context size (0 = use default)
 
+        // std::vector<whisper_token>: tokens to provide the whisper model as initial prompt
+        const whisper_token * prompt_tokens;
+        int prompt_n_tokens;
+
         const char * language;
 
         struct {